The present invention relates generally to the mechanical support of electrical conductors of dynamoelectric machines and, more specifically, to the mechanical support of the end turns of electrical generator stator coils.
Dynamoelectric machines in general, and turbine generators in particular, utilize stator coils which are disposed within axial slots in an associated stator core. These coils extend axially from the core to form end turns where intercoil connections are made which determine the electrical phase associations of the coil assembly. In this end turn region the coils extend from the stator core in both the axial and radial direction in such a way so as to form a conductor configuration in the general shape of a frustum of a cone.
Since the end turns are not supported along their entire length by the core, a means of mechanical support must be provided. It is desirable to firmly attach the end turns to this support apparatus in order to constrain the movement of the end turns and to minimize vibration. However, since the coil end turns are subjected to elevated temperatures, they expand along their length in a direction away from both the stator core's axial end and the core's central axis. Since the straight portion of each coil is essentially constrained in a slot of the stator core, the resulting expansion movement of each segment of the end turn is a function of not only its thermal expansion but that of all other segments between it and the stator core. In other words, the resulting amount of movement of a particular segment of a coil is cumulative and in a direction away from the stator core.
The end turn support means, itself, is also subjected to elevated temperatures and will expand as a dual function of the temperature and its coefficient of thermal expansion. If the support means is fixed at some point, it will experience a similar cumulative expansion with the movement of any point on the support being a function of the distance of that point from the point at which the support means is fixed.
It should be apparent that if the coefficients of thermal expansion of the end turn assembly and the support means are significantly different, relative motion between them can occur. If the end turn assembly and its support means are fastened together in a rigid manner, this relative movement can create stresses in the components and possibly lead to fractures in either the coil insulation or support structure.